The present invention relates to a tibial component for an artificial knee joint.
An artificial knee joint coping with symptoms of a knee comprises a femoral component and a tibial component. In the case where the knee is replaced with the artificial knee joint, joint portions including a distal part of the femur and an proximal part of the tibia, which are to be replaced, are resected, and the femoral component and the tibial component are fixedly inserted respectively into the distal part of the femur and the proximal part of the tibia.
The tibial component of this kind referred to above is known from, for example, Japanese Patent Provisional Publication No. SHO 64-68256. In this case, a stem extends straight downwardly substantially from a center of a lower face of a plate section. Further, a pair of laterally directed triangular fins extend from the lower face of the plate section, at both medial and lateral sides of the stem, and a pair of antero-posteriorly directed fins extend downwardly from the lower face of the plate section at the lateral ends of the respective laterally directed fins. Accordingly, the laterally directed fins and the antero-posteriorly directed fins are formed into a double T-shaped configuration.
The laterally directed fins and the antero-posteriorly directed fins prevent the tibial component from rotation about the longitudinal axis of the tibia. Further, the laterally directed fins support a load in the antero-posterior direction, while the antero-posteriorly directed fins support a load in the lateral direction. Accordingly, the tibial component has such a function as to prevent inclination in the antero-posterior and medio-lateral directions.
However, the above-described tibial component has the following disadvantages. That is, since the tibial component is provided with the two laterally directed and two antero-posteriorly directed fins, the bone is fractioned so that an interruption in blood circulation occurs in the bone. Further, there are many projections or corners of the bone formed by the fins, and the projections or the corners causes the bone necrosis. Moreover, in a case with deep wear in the tibial plateau, the upper end of the tibia has to be osteotomized largely in a horizontal plane, so that the lower downwardly from the upper end of the tibia the level of osteotomy, the more reduced the inner diameter of the tibia. Accordingly, in the component in which, as described above, the laterally directed fins of the tibial component are projected out far away from the central axis of the component, these laterally directed fins may destroy the cortex of the tibia at implantation, and the stability of an implanted component is reduced. Furthermore, since there are many numbers of fins, molding or forming is difficult. Further, since the total cross-sectional area of the fins is larger, driving into the tibia is more difficult.